The present invention relates to a process and to an apparatus permitting the detection and prelocalization of the fracture of a can in a fuel assembly of a fast nuclear reactor cooled by the circulation of a liquid metal, generally sodium, by counting the delayed neutrons emitted by the fission products escaping from the defective assembly and located by the liquid metal.
Provisions have already been made for carrying out a measurement of delayed neutrons due to fission products released as a result of the fracture of a can by passing all or part of the cooling agent flow within the vessel as close as possible to a neutron detector, which is itself located externally of the latter. Neutrons emitted by fission products with a certain delay compared with the initial nuclear reaction in the core therefore have, at the time where they pass in the vicinity of the detector, a harder energy spectrum than that of the neutrons produced in the core. Thus, their detection can be ensured under more reliable and effective measuring conditions making it possible to carry out the necessary interventions on the defective assembly within a shorter period of time.